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Hydrogen and S-Block Element: Physical Properties of Alkali Metals

Physical Properties of Alkali Metals

  • As we go down the group the alkali metals show steady increase in size due to the addition of a new shell at each step.
  • The increase in size of the atoms or ions, directly influences the physical and chemical properties of the alkali metals.

Some physical properties are given in Table:

Illustration: Physical Properties of Alkali Metals

Trends in physical properties are listed in Table:

Illustration: Physical Properties of Alkali Metals

Chemical Properties of Alkali Metals

Oxides

  • All alkali metals form oxides, which are basic in nature.
  • Lithium forms only one type of oxide, lithium monoxide because Tiny lithium ion is not able to come in contact with sufficient number of per oxo ions.
  • Sodium peroxide is formed when sodium is heated with oxygen.
  • Other metals of this group also form superoxide՚s on reaction with oxygen.

Reactivity Towards Water

All the metals of this group react with water explosively to form hydroxide and liberate hydrogen.

  • The lithium has most electronegative but the reaction with water is considerably less vigorous than that of sodium which has the least negative among the alkali metals.
  • The low reactivity of lithium is due to small size and high ionization enthalpy.

Basic character of oxides and hydroxides:

The basic character of oxides and hydroxides of alkali metals increases with the increase in size of metal ion.

Hydrides

The alkali metals react with hydrogen at about to form hydrides , where stands for alkali metals.

Halides

Alkali metals react with halogens to form halides: